The present invention relates to the field of touch switch arrangements.
Many touch switch arrangements are known for controlling a variety of systems. Generally, touch switch arrangements may be categorized as either having or not having a direct electrical connection between a touch plate and the portion of the system to be controlled. The latter type may be more desirable than the former for use with systems, such as television receivers, which generate relatively high operating voltage and which may therefore require electrical isolation between user controls and the controlled portion.
Typically, touch switch arrangements which do not have a direct electrical connection between a touch plate and the controlled portion are of a capacitive type. In such arrangements, when a user touches a touch plate, the capacitance of a touch sensitive capacitive network is changed. A sense circuit detects the change in capacitance and causes the controlled portion to be appropriately controlled. This may, for example, be accomplished by detecting the change in amplitude of an alternating signal coupled through the touch sensitive capacitive network.
Serious consideration must be given to interconnections employed in capacitive types of touch switch arrangements. Interconnections may exhibit appreciable stray capacitances which may adversely affect the operation of touch switch arrangements. To ensure that stray capacitances associated with interconnections employed in capacitive type of touch switch arrangements are relatively low and relatively consistent from unit to unit, the interconnection configuration may be rigidly controlled, for example, by means of printed circuit techniques. In addition, to minimize the adverse effects of whatever stray capacitances remain, it may be necessary to employ special active sense circuits, such as keyed and differential amplifiers, preferably physically located in close proximity to the touch sensitive capacitive network.
Unfortunately, such measures may not be compatible with systems, such as television receivers, in which it is desired to incorporate as much active signal processing circuitry as possible in a single location, such as on a printed circuit board, to reduce cost and increase reliability by minimizing the number of connectors and interconnecting wires. Because of the physical configuration of television receivers, user controls are typically remotely located from the signal processing circuitry thereby necessitating relatively long interconnection wires. As a result, it is relatively difficult to rigidly control the interconnection configuration and impracticable to have active circuits near the user controls.
Not only do relatively long interconnecting wires have stray capacitances which may adversely affect the operation of capacitive touch switch arrangements, but in addition, relatively long interconnecting wires tend to radiate interference signals in response to alternating signals coupled through them to and from the capacitive touch switch arrangement which may adversely affect the performance of a television receiver itself. Thus, there is a requirement for touch switch arrangements of the capacitive type suitable for systems such as television receivers.